Hypodermic syringe with clutch for aspiration

ABSTRACT

A hypodermic syringe by which aspiration as well as injection can be effected, for example for the purpose of testing to see if the cannula has been inserted into a correct tissue of the patient. The syringe includes an operating lever for engaging a clutch acting between the piston rod or plunger of the syringe and a slide mounted co-axially on the piston rod and slidable thereon in a housing formed by part of the body of the syringe. The clutch can be released or engaged by the user while he is gripping the piston rod with the same hand, and thereby he can readily control the aspiration volume.

United States Patent 1 Schmidt HYPODERMIC SYRINGE WITH CLUTCH FORASPIRATION [75] Inventor: Gunther Schmidt, Eschwege,

Germany [73] Assignee: M. Woelm, Eschwege, Germany [22] Filed: Oct. 27,1971 [21] Appl. No.: 192,990

[30] Foreign Application Priority Data Oct. 29, 1970 Germany ..l 2053096Apr. 22, 1971 Germany 2119508 [52] US. Cl. 128/218 R, 128/218 PA [51]Int. Cl A6ln 5/22 [58] Field of Search 128/215,218 R,218 P, 128/218 PA,218 D, 218 F, 2 F, DIG. 5, 276,

[56] References Cited UNITED STATES PATENTS 2.585815 2/1952 McLintock128/218 C 1.718.596 6/1929 Smith 128/218 D 3.583.399 6/1971 Ritsky...128/218 D 3224.445 12/1965 Melott 128/218 D [4 1 Mar. 19, 1974 2,892,4576/1959 Sturtz 128/218 R 3.340.872 9/1967 Cox 128/218 D 3.528,404 9/1970Chan 128/276 X 3,035,605 5/1962 Ninnelt 222/153 X FOREIGN PATENTS ORAPPLICATIONS 1,278,702 9/1968 Germany 128/218 R 31,681 12/1926 France128/218 D Primary ExaminerRichard A. Gaudet Assistant Examiner--J. C.McGowan Attorney, Agent, or F irm-Salter & Michaelson 5 7 ABSTRACT Ahypodermic syringe by which aspiration as well as injection can beeffected, for example for the purpose of testing to see if the cannulahas been inserted into a correct tissue of the patient. The syringeincludes an operating lever for engaging a clutch acting between thepiston rod or plunger of the syringe and a slide mounted co-axially onthe piston rod and slidable thereon in a housing formed by part of thebody of the syringe. The clutch can be released or engaged by the userwhile he is gripping the piston rod with the same hand, and thereby hecan readily control the aspiration volume.

16 Claims, 12 Drawing Figures PAIENIEBMAR 19 1974 SkiEH 2 BF 4 Pmmwm 1 9mm shame? SHEEI M 0? 4 HYPODERMIC SYRINGE WITH CLUTCH FOR ASPIRATIQN Theinvention concerns a hypodermic needle of the kind having means foraspiration, provided with a swivelling operating lever at the handle endof the syringe housing, the operating lever being movable intoengagement with the piston rod for aspiration against the force of areturn spring.

In the case of repeated injections it is necessary for medical reasonsfor the person giving the injections to make sure, after penetratingwith the injection cannula that the correct tissue was entered. This isdone by aspiration immediately after puncturing. For this purpose, thepiston of the syringe is pulled back slightly thus drawing blood fromthe body to obtain an idea, by observing the type and quantity of blood,in which tissue the point of the cannula is located. Injection can onlybe made after a blood check by aspiration.

Aspiration with commercial-type hypodermic syringes presentsdifficulties particularly in cases where specially sensitive tissuesmust be punctured and also when relatively restricted space is availablefor handling the syringe. This is a regular experience in medicine.

In a hypodermic syringe of a known type, a doublelever is arranged on aswivel pin located in a slot on the finger grip piece of the syringehousing, extending at an acute angle to the piston rod axis of thesyringe in such a way that the swivel bearing is moving in the slottowards the piston rod. The piston rod is also provided with teeth overwhich one end of the double-ended lever can be engaged against the forceof a spring, by pressing on the other arm of the double-ended lever. Ina known design, a danger exists of the aspiration lever jamming againstthe piston rod of the syringe during operation.

It is also known to provide a spring on the piston rod of a syringe, thespring acting together with an opposing bearing which is connected withthe piston rod over a friction connection. In this case, the spring ispreloaded when the piston rod is pushed forward, the preloading forcecorresponding to the friction force of the connection with the pistonrod. If the grip is released on the piston rod of such a syringe, thepiston of the cylindrical ampoule is pulled back under spring pressureand aspiration thus takes place. The disadvantage of this syringe liesin the fact that friction is acting against the movement of the pistonrod during the whole injection process and also in that pre-tensioningof the spring is a necessary condition for the aspiration movement,pre-tensioning only being capable of being performed by shifting thepiston rod in the direction of the injection movement.

Furthermore, a syringe with an aspiration device is known in which afurther axially movable rod is arranged parallel to the piston rod, atthe syringe housing. The piston rod and the rod arranged parallel to itare both provided with teeth and are coupled by a reversing gear. Bypressing on the parallel rod, the piston rod can be pulled back thusproducing aspiration. Such an arrangement requires a great deal of spaceand a further disadvantage is presentedby the fact that the rodextending parallelto the piston rod is moving to the outside at the samespeed as the piston moves inwards during injecting.

The purpose of the invention is to create a hypodermic syringe of theaforesaid kind which would allow aspiration with the piston rod in anyposition without the danger of jamming or blocking and ensure afreemovement for the piston rod during injection.

According to the invention, a hypodermic syringe having means foraspiration and including a piston rod, a return spring therefor and anoperating lever engageable in the piston rod to move the piston rodagainst the force of the return spring for the purpose of aspirationalso includes a slide slidable on the piston rod on movement of theoperating lever and clutch means provided between the slide and thepiston rod.

Conveniently the slide is a frusto-conical bore widening towards the endof the piston rod to be gripped by the user and the syringe alsoincludes a plurality of balls acting as clutch elements and positionedin the annular space between the frusto-conical bore of the slide andthe piston rod, said balls being urged to grip the piston rod by wedgingaction of the frusto-conical bore on axially moving the slide in thedirection to reduce the radial clearance between the bore and the pistonrod, and a stop member which extends into the conical bore when theslide has been moved to the position in which the balls are freed fromengagement between the piston rod and the frusto-conical bore andresilient means for urging the balls into engagement with the stopmember, which thereby forms a support for the balls when-the clutchmeans has been released.

The syringe may include a housing into which the slide is movable, saidhousing provided with diametrically-opposite slots extending axially ofthe housing and each receiving stub shafts pointing in oppositedirections to each other on the operating lever, said stub shaftsextending through the slots in the housing into blind holes in saidslide.

The fulcrum of the operating lever may be provided by a fixed abutmentagainst which the lever swivels and spaced from the axis of said stubshafts. The fixed abutment may be positioned between the stub shafts andthe end of the lever to be engaged by the user. The operating lever mayalterantively be a double-arm lever and said fixed abutment may beengaged by the end of the operating lever remote from that end which isto be gripped by the user. Conveniently the operating lever may includea frame part of substantially rectangular shape surrounding the slidehousing. The operating lever may be pivotally mounted on the slidehousing at the end of the lever remote from the end thereof which is to.be gripped by the user and said slide may include tenons engaging thelever in such a way that the clutch is engaged when the lever is pulledtowards the end of the piston rod that is gripped by the user.

The syringe may include spring means acting to urge the slide in thedirection in which said clutch means is released.

The syringe may include a pair of fixed stops between which the slide ismovable.

Several versions of hypodermic syringe of the aforesaid kind inaccordance with the invention, are illustrated in the accompanyingdrawings and are described in detail with reference thereto. In thedrawings:

FIG. 1 shows a side view of a hypodermic syringe with an aspirationdevice having a cylindrical ampoule;

FIG. 2 shows the same view as in FIG. 1 except that part of it is shownin section;

FIG. 3 shows the head of the syringe shown in FIGS. 1 and 2 in thenormal working position from which aspiration can be effected with thepiston rod in any position;

FIG. 4 shows the same view as FIG. 3 but with the piston rod retractedby the aspiration device;

FIG. 5 shows the aspiration device in section along the line V-V in FIG.3, and to an enlarged scale;

FIG. 6 shows the aspiration device in section along the line VI-VI inFIG. 4, and to an enlarged scale;

FIG. 7 shows the head of an injection syringe, similar to that shown inFIG. 3, but having an aspiration device shown in its normal workingposition of another version in accordance with the invention;

FIG. 8 shows the hypodermic syringe shown in FIG. 7 during aspiration;

FIG. 9 shows the head of a third version of hypodermic syringe inaccordance with the invention, similar to that shown in FIGS. 3 and 7and having an aspiration device in its normal working position;

FIG. 10 shows a section along line XX in FIG. 9;

FIG. 1 1 shows a side view of a fourth version of a hypodermic syringein accordance with the invention, having an aspiration device in itsnormal working position, and

FIG. 12 shows a longitudinal section through the hypodermic syringeshown in FIG. 11 along the line XIXI therein.

The version of hypodermic syringe shown in FIGS. 1 and 2, is of the kindto be loaded with cylindrical ampoules. The parts of the syringe locatedbelow the line 6-6, including the piston rod and the hand grip, areknown. The syringe comprises a housing 8 provided with an aperture 12extending longitudinally thereof and intended for inserting and removingthe cylindrical ampoule 10.

A removable holder 14 for the injection needle 16 is screwed on to thelower end of the syringe housing 8. The uppwer end of the syringehousing contains a bellshaped holder 18 for the cylindrical ampoule 10.The holder 18 is axially movable and is urged downwardly as viewed inFIG. 2 by a spring 20. A piston rod guide 22 in which the axiallymovable piston rod 24 is located engages in the upper end of the syringehousing 8. The piston rod 24 carries at its lower end a stop piece 26which in turn carries a screwed shoulder 28. The piston rod guide 22also serves as a holder for a finger grip piece 30 which is clamped by athreaded bush 32 screwed on to the outside of the syringe housing 8.

In order to prepare the syringe juste described for an injection, thepiston rod 24 is withdrawn by means of the hand grip 34; and at the sametime the bell-shaped holder 18 is withdrawn over the shoulder 26. Acylindrical ampoule can then be inserted through the side opening intothe syringe housing and axially fixed and centred in the housing byreleasing the hand grip 34. By turning the hand grip 34 and the pistonrod 24, the screwed shoulder 28 of the piston rod is then screwed into atapped bore in the closing piston 33 of the cylindrical ampoule.Aspiration can then be effected by pulling the hand grip 34 andinjection follows on depressing the hand grip.

The aspiration device 36 in accordance with the invention is locatedabove the finger grip piece 30 and is now described in detail withparticular reference to FIGS. 5 and 6.

The piston rod guide 22 is provided with an external thread 37 above thestop for the finger grip piece, on

end of the syringe. A number of clutch balls 52 pressure-loaded througha washer 54 from a resilient element 56 are spaced around the peripheryof the piston rod 24 in the bore 48. The bottom diameter of the bore 48is smaller than the diameter of the piston rod 24 plus twice thediameter of each clutch ball 52. The piston rod guide 22 has at itsupper end an annular shoulder 58 having an outside diameter which issmaller than the bottom diameter of the bore 48 of the slide 40. Thisannular shoulder can therefore enter the bore 48.

Te aspiration device also comprises the operating lever 60 attached tothe pot-shaped housing 38 in such a way that the lever 60 can swivel andengage the slide whereby the slide can be moved from the position shownin FIG. 5 to the position shown in FIG. 6. In the illustrated version ofthe design, the operating lever 60 is roughly formed in the shape of aU-strap, the ends of which are bent inwardly. These bent ends engagethrough two diametrically opposed slots 62 in housing 38 into the holes64 of the slide 40. The operating lever 60 is thus connected with theslide in such a manner that it can swivel.

A plate 66 acting as a fixed abutment bearing and provided with recesses68 is attached on the outside of the housing 38 at a radial distancefrom the axis of the housing. The lever rests with its limbs in theseopenings, while the edges of the recesses form abutment bearings betweenwhich the operating lever 60 swivels. The operating lever 60 is able toslide in the longitudinal direction of its limbs during this swivellingmovement.

It would alternatively also be possible to locate the operating lever 60at a fixed swivelling point on the housing and to provide at the slide40 pins protruding through the openings 62 and engaging the operatinglever.

The normal position of the aspiration device is that shown in FIG. 5.Here, the thrust spring 44 holds the slide 40 against the upper edge ofthe piston rod guide 22. The annular shoulder 58 engages into the bore48 and presses the clutch balls 52 upwardly, as viewed in FIG. 5,against the axial force of the resilient element 56. At the same time,the operating lever 60 is tilted by the upward force of the spring 44.The piston rod 24 is freely movable axially in both direction.

When aspiration is to take place, pressure must be exerted on the gripend of the operating lever 60 in a direction away from the hand grip 34.This causes the slide 40 to be shifted upwards against the force of thespring 44. The clutch balls 52 are then released from engagement withthe annular shoulder 58 and are caused to be clamped, by the resilientelement 56, between the conical wall and the piston rod 24. As a resultof the wedge effect which is thus caused, the forces required forwithdrawing the piston rod and the ampoule piston fixed to it aretransmitted to the piston rod. The aspiration volume therefore dependssolely on the extent of the swing movement of the operating lever and iseasily controllable.

After aspiration, the operating lever 60 is released and the slide 40 isreturned to its starting position as shown in FIG. 5, under the pressureof the spring 44. The wedging effect of the clutch balls 52 is thuseliminated immediately this movement starts so that no axial forces areexerted by the aspiration device on the piston rod in the direction ofthe ampoule. n the last phase of the releasing movement of the lever 60,the annular shoulder 58 enters the bore 48 and presses the clutch balls52 against the resilience of the element 56 sufficiently to provideclearance around the balls 52 between the conical walls 50 and thepiston rod 24.

FIGS. 7 and 8 shows the head only of the second version of thehypodermic syringe. The clutch means of the aspiration device inthisversion of the syringe is generally the same as in the aspirationdevice 36 in the first version. Therefore, the same references but withthe prefix 1 areused for those somponents which are the same for thefirst version.

The aspiration device 136 comprises a piston rod guide 122 with a fingergrip piece 130 mounted on it and held by a threaded bush 132. Tepistonrod guide 122 has a pot-shaped housing 138 screwed over it in which aclutch slide similar to that of the first version is arranged coaxiallywith the piston rod 124 and by which a thrust spring 144 is held in itsidle position. Two openings 162 facing each other are formed in sideflats in the housing 138. The operating lever 164 is designed as adouble lever and engages with two legs on the side past the pot-shapedhousing 138. The operating lever is provided with a swivel joint havingaxle pins 167, each formed by the pin protruding inwards and engaging inthe appropriate bore in the clutch slide. Further details are describedhereinafter with reference to FIGS. 8 and 10. The lever arm of thedouble-arm lever 164 shown in FIGS. 7 and 8 is formed in the shape of agrip 169 in which the actual gripping piece is formed as a flat justabove the finger grip piece 130. The oppositelever arm 170 extends pastthe outside periphery of the housing 138 and rests loosely on anabutment 172 attached to'the outside of the housing 138. In order tokeep the abutment 172, the supporting face of which faces the grip piece134 of the piston rod 124, as narrow as possible, the two legs of the,doublearm lever are interconnected at the end of the arm 170 by means ofa cross stay which is not shown in the drawing.

In the position shown in FIG. 7, the aspiration device 136 is disengagedfrom the piston rod 124 so that the piston rod 124 can move freely inboth directions. For making an injection, the syringe is gripped as inFIG. 8 in such a way that the grip piece 134 rests under the thumb whilethe index finger and the middle finger grip under the ends of the fingergrip piece 130. After the cannula of the syringe, held in this way, haspenetrated the patients tissue, the third finger which is bent under thegrip end 169 of the operating lever 164 can pull the operating leverupwards as viewed in FIG. 8. At the same time, the operating lever 164is resting with the end of its lever arm 170 on the abutment 172 so thatthe clutch slide is lifted over the axle pins 167 thus causing theclutch to become effective. The jacking end of the lever arm 170 shiftsat the same time slightly radially inward since the pins 167 and thusthe swivel joint of the operating lever 164 are guided in the paralleldirection over the clutch slide. The support face at the end of thelever arm 170 is suitably bent, as shown in the drawing.

Aspiration can then be sensitively adjusted by pulling the grip end 169of the operating lever with a greater or lesser force. Particularadvantage is presented by the fact that when the operating lever ispulled with the third finger, the piston rod is relieved automaticallyby the reduction of pressure exerted on the hand grip 134 withoutcreating instability of the syringe in the hand.

After aspiration, the operating lever 164 is released. The clutch slideis then moved back automatically by the spring 144 to its declutchedposition. At the same time, the piston rod 124 is released so thatinjection can follow immediately without changing the position of thesyringe in the hand in any way whatsoever.

While the axle pins 167 forming the swivel joint for the operating leverin the version shown in FIG. 7 are arranged at the same place and engagethe clutch slide, just as in the version shown in FIGS. 1 to 6, FIGS. 9and 10 show a third,'different version of thesyringe. In FIGS. 9 and 10,common parts are again given the same reference numbers as in FIGS. 1 to8 but with pre-fix With reference to FIGS. 9 and 10, the operating lever274 is formed in the shape of a double-arm lever just as in the versionshown in FIGS. 7 8. The lever 274 is arranged immediately above thefinger grip piece 230 on the upper face of which a plate 276 is located.The latter is formed for example, in one piece with the piston rod.guide and it being possible, for example, to screw the finger grip piece230 to the plate 276. A can be seen from FIG. 10, the operating lever274 is formed in the shape of a frame which is roughly rectangular andcan be made from profiled wire, the ends of this profile wire beingclosed together in the center of the wire and then welded together toform the grip 278.

Tenon screws 282 are screwed into the two parallel members 280, withtheir tenon ends 284 engaging in the bores in a lower portion of theclutch slide 240. The plate 276 serves as an abutment on which the leverarm 286, lying opposite to the grip 278, rests with a connection stay288.

The operation of thisaspiration device is the same as that shown inFIGS. 7 and 8, so that the same explanations apply in this case. Thearrangement shown. in FIGS. 9 and10 is characterised by greatersimplicity than that shown in FIGS. 7 and 81. As in the case of theversions shown in FIGS. 7 and 8 the point of support of the operatinglever slides towards the axis of the piston.

In a further modification, the operating lever can be connected by itsends, which is opposite to the grip,

over a fixed swivel joint with the housing. In this version of thesyringe, the clutch slide can be provided with driver pins protruding tothe outside which either engage in slots in the operating lever or reston the upper face of the operating lever. In order to keep transverseforces exerted at the clutch slide as low as possible a slot or asupport face can be arranged at or on the operating lever in such a waythat the force exerted by the lever on the tenons at the clutch slide,with the operating lever in its central position, is exactly parallel tothe axis.

The part of the syringe to be supplemented underneath the grip piece or230 can be formed in the shape of a syringe frame for injectingcylindrical ampoules. However, it is also possible to design the syringeas a normal syringe with a fixed cylinder and with a fixed piston at thebottom end of the piston rod, with which the liquid which is to beinjected is drawn from i a supply bottle or a similar receptacle.

A hypodermic syringe having an aspiration device of adifferent design isshown in FIGS. 11 and 12. The same components, or those giving the sameaction, are in this case again marked with the same reference numbers asin the preceding figures but with the prefix 3. In this version ofsyringe, the piston rod guide 322 is provided with a bush-like collar323 which has an internal thread. The upper end, provided with anexternal thread, of a metal bush 325 is screwed into the bush. The bush325 is provided with side apertures, and has at its lower end aninwardly facing flange 327 with which a needle holder 329 is held. Asyringe cylinder 331 made from glass or plastics is clamped between thepiston rod guide 322 and the needle holder 329 in such a way that thecylinder rests against the needle holder forming a seal at that point.The cylinder 331 contains a ground piston 333 which is provided with athreaded bore into which the piston rod 324 is screwed, the lattercarrying the grip piece 334 at its outer end. The piston rod guide 322is formed with a peripheral flange 319 engaged underneath by a grippiece 330. A flange 337 at the lower end of the pot-shaped housing 338rests on top of the flange 319. The pot-shaped housing 338 and thefinger grip piece 330are connected with the flange 319 of the piston rodguide 322 by means of screws 339. The clutch slide 340 is axiallymovable in the potshaped housing 338 and has a conical bore 350extending from the bottom end of the slide and widening upwards. Thisbore contains clutch balls 352 which, when released, as shown in FIG.12, rest on an annular shoulder 358 of the piston rod guide 322. Theballs 352 engage underneath a tube 354 which extends through the slideand on which one end of a helical spring 359 is supported. The other endof the spring 359 is supported under a ring 361 against the outer end346 of the potshaped housing 338. A spring 344, coaxial with the spring359, is supported with one end against the slide 340 and the otheragainst the end 346 of the potshaped housing 338. The clutch slide 340is provided with diametrically opposite bores 341 in which the operatinglever 374 designed as a double-arm lever can swivel, just as in theversions shown in FIGS. 7 to 10. Just as in the version shown in FIGS. 9and 10, this operating lever 374 is suitably formed as a rectangularframe which can be produced from profiled wire, the ends of thisprofiled wire being closed together at the centre of the wire andriveted or screwed together thus forming a grip 378. Tenon screws 382are screwed into the two parallel members 380 of the operating lever374, engaging with their tenon ends 384 in bores 341 of clutch slide340. The flange 337 of this version serves also as the abutment bearingfor the operating lever 374 on which the operating lever is supported byits arm opposite to the grip-378, again preferably by a connection stay388. The operation of the version of hypodermic syringe shown in FIGS.11 and 12 is similar to those shown in FIGS. 7 to 10.

In order to perform an injection, with any one of the foregoing versionsof syringe having an aspiration device in accordance with the invention,the syringe is taken in the hand and the point of the cannula isinserted into the tissue. To perform the subsequent checking aspiration,the piston rod is retracted through the clutch of the aspiration devicewith the aid of the operating lever, presure on the piston rod beingsimultaneously stopped. At the same time, the operating lever is pushedaway from the grip of the piston rod as in the version of the designshown in FIGS. 1 to 6, or pulled to the grip end of the piston rod, asin FIGS. 7 to 12, the latter versions of the syringe providing theadvantage of steadier handling. If aspiration shows that the correcttissue has been entered, injection can be made immediately afterreleasing the operating lever. If the aspiration check is negative, thepenetration depth can be corrected at the-same entry point or anotherpuncture, followed by checking aspiration, can be made at another point.

It frequently happens, in particular in dentistry that injections atvarious points are made with the same ampoule contents. The aspirationdevice in accordance with the invention makes it possible to make thenecessary aspiration check on each penetration and independently of theposition of the piston rod.

What I claim as my invention and desire to secure by Letters Patent ofthe United States is:

l. A hypodermic syringe having an aspiration device, the syringeincluding a housing with finger grip means attached thereto, a pistonrod slidably positioned in said housing and extending therefrom, a handgrip attached to the extending end of the piston rod and means on oneend of the said housing for attaching a hypodermic needle, and theaspiration device comprising a second housing connected to the other endof said syringe housing and slidably receiving the extending portion ofsaid piston rod, a slide member within said second housing which isslidable coaxially with the piston, an operating lever connected to saidslide member, said slide member responsive to movement of said lever, aspring for returning the slide member to an initial position afterreleasing the operating lever and a clutch provided between the slidemember and the piston rod and operable by the slide member to engage theslide member with the piston rod, whereby the piston rod is moved inresponse to movement of the operating lever for the purpose ofaspiration. v

2. A syringe as claimed in claim 1 in which the slide member has afrusto-conical bore widening towards the end of the piston rod to begripped by the user, the clutch including a plurality of balls acting asclutch elements and positioned in an annular space between thefrusto-conical bore of the slide and the piston rod, said balls beingurged to grip the piston rod by wedging action of the frusto-conicalbore pursuant to axial movement fo the slide in a direction to reducethe radial clearance between the bore and the piston rod, and a stopmember which extends into the conical bore when the slide member hasbeen moved to its initial position and by which the balls are held freefrom engagement between the piston rod and the frustor-conical bore,said stop member forming a support for said balls.

3. A syringe as claimed in claim 2 in which the slide member is movablein a housing, the housing being provided with diametrically-oppositeslots extending axially of the housing and through which the operatinglever is connected to the slide member.

4. A syringe as claimed in claim 3 further comprising resilient meansfor urging the balls into engagement with the stop member.

5. A syringe as claimed in claim 4, said resilient means comprising anaxially compressible resilient ring provided in the housing around thepiston rod and engageable between the balls and the slide member.

6. A syringe as claimed in claim 3 in which stub shafts are provided onthe operating lever, the stub shafts extending in opposite directions toeach other through the slots in the housing into blind holes in theslide member.

7. A syringe as claimed in claim 6 in which a fulcrum for the operatinglever is provided by a plate defining a fixed abutment spaced from theaxis of the stub shafts and against which the lever can be swivelled.

8. A syringe as claimed in claim 7 in which the plate defining the fixedabutment is positioned between the stub shafts and the end of theoperating lever to be gripped by the user.

9. A syringe as claimed in claim3 in which the operating lever comprisestwo arms in the form of a fork, the end of the arms remote from the endwhich is to be gripped by the user being engageable with a fixedabutment.

10. A syringe as claimed in claim 9 in which said fixed abutment is aflat surface provided on the outside of the housing.

11. A syringe as claimed in claim 3 in which the operating lever isformed in the shape of a substantially rectangular frame surrounding thehousing.

12. A syringe as claimed in claim 3 in which the operating lever ispivotally mounted on the housing at the end thereof remote from the endwhich is to be gripped by the user, the slide member including pinsprojecting through the slots in the housing and being engageable withthe lever in such a way that the clutch will be engaged when the leveris pulled towards the end of the piston rod that is to be gripped by theuser.

13. A syringe as claimed in claim 2 in which movement of the slidemember to its initial position by the return spring releases the clutchto disconnect the slide member from the piston rod.

14. A syringe as claimed in claim 13 in which the return spring for theslide member is a compression spring co-axially mounted on the pistonrod and acting between the housing and the slide member.

15. A syringe as claimed in claim 2 including a pair of fixed stopsbetween which the slide member is movable.

16. A syringe as claimed in claim 4, said resilient means comprising asecond spring positioned co-axially within the slide-returning spring.

1. A hypodermic syringe having an aspiration device, the syringeincluding a housing with finger grip means attached thereto, a pistonrod slidably positioned in said housing and extending therefrom, a handgrip attached to the extending end of the piston rod and means on oneend of the said housing for attaching a hypodermic needle, and theaspiration device comprising a second housing connected to the other endof said syringe housing and slidably receiving the extending portion ofsaid piston rod, a slide member within said second housing which isslidable coaxially with the piston, an operating lever connected to saidslide member, said slide member responsive to movement of said lever, aspring for returning the slide member to an initial position afterreleasing the operating lever and a clutch provided between the slidemember and the piston rod and operable by the slide member to engage theslide member with the piston rod, whereby the piston rod is moved inresponse to movement of the operating lever for the purpose ofaspiration.
 2. A syringe as claimed in claim 1 in which the slide memberhas a frusto-conical bore widening towards the end oF the piston rod tobe gripped by the user, the clutch including a plurality of balls actingas clutch elements and positioned in an annular space between thefrusto-conical bore of the slide and the piston rod, said balls beingurged to grip the piston rod by wedging action of the frusto-conicalbore pursuant to axial movement fo the slide in a direction to reducethe radial clearance between the bore and the piston rod, and a stopmember which extends into the conical bore when the slide member hasbeen moved to its initial position and by which the balls are held freefrom engagement between the piston rod and the frustor-conical bore,said stop member forming a support for said balls.
 3. A syringe asclaimed in claim 2 in which the slide member is movable in a housing,the housing being provided with diametrically-opposite slots extendingaxially of the housing and through which the operating lever isconnected to the slide member.
 4. A syringe as claimed in claim 3further comprising resilient means for urging the balls into engagementwith the stop member.
 5. A syringe as claimed in claim 4, said resilientmeans comprising an axially compressible resilient ring provided in thehousing around the piston rod and engageable between the balls and theslide member.
 6. A syringe as claimed in claim 3 in which stub shaftsare provided on the operating lever, the stub shafts extending inopposite directions to each other through the slots in the housing intoblind holes in the slide member.
 7. A syringe as claimed in claim 6 inwhich a fulcrum for the operating lever is provided by a plate defininga fixed abutment spaced from the axis of the stub shafts and againstwhich the lever can be swivelled.
 8. A syringe as claimed in claim 7 inwhich the plate defining the fixed abutment is positioned between thestub shafts and the end of the operating lever to be gripped by theuser.
 9. A syringe as claimed in claim 3 in which the operating levercomprises two arms in the form of a fork, the end of the arms remotefrom the end which is to be gripped by the user being engageable with afixed abutment.
 10. A syringe as claimed in claim 9 in which said fixedabutment is a flat surface provided on the outside of the housing.
 11. Asyringe as claimed in claim 3 in which the operating lever is formed inthe shape of a substantially rectangular frame surrounding the housing.12. A syringe as claimed in claim 3 in which the operating lever ispivotally mounted on the housing at the end thereof remote from the endwhich is to be gripped by the user, the slide member including pinsprojecting through the slots in the housing and being engageable withthe lever in such a way that the clutch will be engaged when the leveris pulled towards the end of the piston rod that is to be gripped by theuser.
 13. A syringe as claimed in claim 2 in which movement of the slidemember to its initial position by the return spring releases the clutchto disconnect the slide member from the piston rod.
 14. A syringe asclaimed in claim 13 in which the return spring for the slide member is acompression spring co-axially mounted on the piston rod and actingbetween the housing and the slide member.
 15. A syringe as claimed inclaim 2 including a pair of fixed stops between which the slide memberis movable.
 16. A syringe as claimed in claim 4, said resilient meanscomprising a second spring positioned co-axially within theslide-returning spring.